OAuth — Basic Credentials
The preferred way to authenticate to Splitit is with basic credentials, which Splitit uses in an OAuth flow under the hood. To accomplish this, each call to a Splitit API must include your API Username and API Password (find here), Base64-encoded and added as a basic authorization header.
Adding Credentials in Standard API Applications
Adding Creds with a Header
If you are using an API application like Postman or Insomnia, you can simply enter in your API Username and API Password under Authorization -> Type -> Basic Auth (Postman) or Auth -> Basic Auth (Insomnia).
To add your credentials in a basic authorization header, first you'll need to encode them to Base64 using a converter such as this one. The format to encode is "API Username:API Password."

Add them to your API call with a header that has a key of Authorization and a value of Basic {your encoded string}:

A cURL example, which calls Initiate

curl --request POST \
--url https://webapi.sandbox.splitit.com/api/InstallmentPlan/Initiate \
--header 'Authorization: Basic QVBJVXNlcjAwMDAzMjIwMDp0QjJyam9XeTdjWDdiQnlkTUZiWWo2UUZ2OFU5M1NvWlBZeHdTdFN3TVhqUTVYZTJaMA==' \
--header 'Content-Type: application/json' \
--cookie 'nlbi_2179264=QbGiHiheewS5650nvrfigAAAAAB6ooyyW4XE0FrcQ0S94JXZ; visid_incap_2179264=UsBokfb1QnemcgrbLfeEP253%2FGEAAAAAQUIPAAAAAACB%2F%2BAWx7fdrcJmzBvXSyFA; incap_ses_1443_2179264=PY3tYaWTwA%2BcZhKiPJEGFJzND2MAAAAABAOiB9sJpuf%2BC0ZBDxZS4A%3D%3D; incap_ses_1543_2179264=HhPUOGRSlx53tLNohtZpFb7EEGMAAAAA40VuO32oNEro8sbsQYaEOA%3D%3D' \
--data '{
"RequestHeader": {
"ApiKey": "5cd8554d-6978-47f3-9e19-97cbc06c14f1",
"PlanData": {
"Amount": {"Value": 121,"CurrencyCode": "USD"},
"RefOrderNumber": "xxxxxx",
"AutoCapture": true,
"ExtendedParams": {
"AnyParameterKey1": "AnyParameterVal1",
"AnyParameterKey2": "AnyParameterVal2"
"BillingAddress": {
"AddressLine": "1st Street",
"AddressLine2": "Apartment 1",
"City": "New York",
"State": "NY",
"Country": "USA",
"Zip": "10016"
"ConsumerData": {
"FullName": "John Smith",
"Email": "[email protected]",
"PhoneNumber": "1-844-775-4848",
"CultureName": "en-us"
"CreditCardDetails": {
"CardCvv": "123",
"CardHolderFullName": "John Smith",
"CardNumber": "4111111111111111",
"CardExpYear": "2029",
"CardExpMonth": "8"
"PaymentWizardData": {
"RequestedNumberOfInstallments": "1,2"
"RedirectUrls": {
"Succeeded": "http://localhost/Succeeded",
"Failed": "http://localhost/Failed",
"Canceled": "http://localhost/Canceled"
"EventsEndpoints": {
"CreateSucceeded": "https://www.async-success.com/"
"DisplaySchedules": true
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