Which direction does data move between Deltek and PayPal?

The main flow is Deltek into PayPal and back. Approved AP invoices and vendor records move from Deltek to create PayPal payout batches, and PayPal captures, refunds, and fees flow back into Deltek as payment records and journal entries. Deltek stays the system of record because PayPal has no vendor master or general ledger.

How does the integration reconcile a PayPal payment to the right Deltek bill?

ml-connector writes the Deltek invoice number into the merchant-supplied invoice_id field when it creates a PayPal payout. When PayPal reports the capture through a webhook or transaction search, that same invoice number identifies the Deltek bill it paid. The matching payment record and journal entry are then posted in Deltek without manual lookup.

How are duplicate payments and Deltek's lack of an idempotency key handled?

PayPal payouts carry a sender_batch_id and each payment a PayPal-Request-Id, so PayPal returns the original result instead of paying twice on a retry. Deltek has no native idempotency header, so ml-connector checks for an existing payment or invoice before posting. Together these stop both double payouts and duplicate ledger entries.

DeltekPayPal

Deltek and PayPal integration

Deltek Vantagepoint runs project accounting, AP, and the general ledger. PayPal moves the money out to vendors and collects payments in. Connecting the two lets approved vendor bills in Deltek pay out through PayPal Payouts without re-keying account details, and lets every PayPal capture and fee come back into Deltek as a payment record and journal entry. ml-connector handles the very different APIs on each side and reconciles each transaction to the Deltek invoice it paid. The result is a closed loop between the ledger and the payment rail.

How Deltek works

Deltek Vantagepoint exposes firms (vendors and clients), employees, projects, AP invoices, AR invoices, journal entries, vendor payments, cash receipts, and GL accounts through a REST JSON API on a tenant-specific URL such as https://acme.deltekfirst.com/acme/api/. It authenticates with OAuth2 password grant, which must be explicitly enabled in newer versions, and the access token is passed as a bearer on every request. Vantagepoint has no public pub/sub event bus; its webhooks are workflow-triggered callbacks with no HMAC signature, so finance records are read by page-based polling. The older Costpoint product is SOAP and preprocessor-file based rather than clean REST.

How PayPal works

PayPal exposes payouts, invoicing, payments, orders, subscriptions, and transaction search through a REST API at api-m.paypal.com, with v1 and v2 paths depending on the resource. Every call uses an OAuth2 client-credentials bearer token that is cached and reused for its roughly eight-hour lifetime. PayPal is a payments platform, not an accounting system: it has no vendor master, no purchase orders, and no GL accounts, so the merchant-supplied invoice_id field is the link back to an ERP bill. PayPal pushes RSA-SHA256 signed webhooks for payment, payout, and invoice events, and transaction search reads history in windows of at most 31 days.

What moves between them

The main flow runs from Deltek into PayPal and back. ml-connector reads approved AP invoices and their vendor firm records from Deltek and creates PayPal payout batches that pay each vendor, carrying the Deltek invoice number in invoice_id. PayPal then reports captures, refunds, and fees through webhooks and transaction search, and ml-connector posts those back into Deltek as vendor payment records and journal entries against the matching GL account. Reconciliation runs on the invoice number that travels in both directions. PayPal holds no GL or vendor master, so ml-connector never expects accounting structure from PayPal; Deltek remains the system of record.

How ml-connector handles it

ml-connector stores both credential sets encrypted, mints a cached PayPal client-credentials token and refreshes it before the eight-hour expiry, and accepts the full Deltek tenant URL per customer since deltekfirst.com publishes no shared base address. It refreshes the Deltek bearer token when a call returns 401. Vendors are matched first so every payout maps a Deltek firm to a PayPal recipient email, and GL accounts are mapped so each returned payment posts to a valid Deltek account. Because Vantagepoint cloud is effectively pull-only, ml-connector polls AP invoices on a schedule rather than waiting for a push, and it backfills PayPal history in 31-day windows to respect the transaction-search limit. Payouts carry a sender_batch_id and each payment a PayPal-Request-Id so a retry never double-pays, which matters because Deltek has no native idempotency key and requires a duplicate check before posting. Inbound PayPal webhooks are verified with RSA-SHA256 using the certificate from paypal-cert-url, after confirming that URL is a paypal.com domain. Every record carries a full audit trail and can be replayed if a downstream call fails.

A real-world example

A 120-person engineering and consulting firm runs Deltek Vantagepoint for project accounting and accounts payable, and pays a long tail of subcontractors and overseas freelancers who prefer PayPal. Before the integration, accounts payable approved each bill in Deltek, then logged into PayPal to send payouts by hand, then re-keyed the cleared amounts and fees back into the ledger, which left payments unreconciled for days and made month-end close slow. With Deltek and PayPal connected, approved bills pay out through PayPal Payouts automatically, and each capture and fee posts back into Deltek as a payment and journal entry tied to the original invoice. The subcontractor ledger reconciles itself and the manual double entry is gone.

What you can do

Pay approved Deltek AP invoices through PayPal Payouts, carrying the Deltek invoice number into the PayPal invoice_id field.
Post PayPal captures, refunds, and fees back into Deltek as vendor payment records and journal entries on the correct GL accounts.
Reconcile PayPal transactions to Deltek bills automatically using the invoice number that travels in both directions.
Bridge PayPal client-credentials OAuth2 and Deltek tenant-specific password-grant login, refreshing both tokens before they expire.
Prevent double payment with PayPal sender_batch_id and PayPal-Request-Id idempotency plus a pre-post duplicate check on the Deltek side.

Questions

Which direction does data move between Deltek and PayPal?: The main flow is Deltek into PayPal and back. Approved AP invoices and vendor records move from Deltek to create PayPal payout batches, and PayPal captures, refunds, and fees flow back into Deltek as payment records and journal entries. Deltek stays the system of record because PayPal has no vendor master or general ledger.
How does the integration reconcile a PayPal payment to the right Deltek bill?: ml-connector writes the Deltek invoice number into the merchant-supplied invoice_id field when it creates a PayPal payout. When PayPal reports the capture through a webhook or transaction search, that same invoice number identifies the Deltek bill it paid. The matching payment record and journal entry are then posted in Deltek without manual lookup.
How are duplicate payments and Deltek's lack of an idempotency key handled?: PayPal payouts carry a sender_batch_id and each payment a PayPal-Request-Id, so PayPal returns the original result instead of paying twice on a retry. Deltek has no native idempotency header, so ml-connector checks for an existing payment or invoice before posting. Together these stop both double payouts and duplicate ledger entries.

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