All SulPayments services share a single base URL with versioned paths. 
https://api-eu.sulpayments.ch/v1

Seller

Checkout, 3DS, Payouts, Reference data

Payment

Charges and refunds

Query

Orders, payouts and balances lookup

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Authentication

Every request requires a Bearer token issued by the authentication endpoint. 
Authorization: Bearer {token}
Tokens expire after 30 minutes. Re-authenticate before expiration to avoid 401 Unauthorized.