I’m not sure why this has started happening but pretty sure it’s your end.
site is here snipcart
the following api call gets a 422
curl 'https://payment.snipcart.com/api/public/sessions' -X POST -H 'User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:129.0) Gecko/20100101 Firefox/129.0' -H 'Accept: application/json' -H 'Accept-Language: en-GB,en;q=0.5' -H 'Accept-Encoding: gzip, deflate, br, zstd' -H 'content-type: application/json' -H 'x-snipcart-publicapikey: YTMyMmZkODItMDViMy00ZmQ0LThlM2QtNDcxYjNjODZmN2EyNjM4NTk5MTM1OTA0NDA3MTkw' -H 'x-snipcart-referer: https://rose-ash.com/snipcart/#/checkout' -H 'x-snipcart-lang: en' -H 'x-snipcart-version: 3.0' -H 'api-version: 2020-04-28' -H 'Origin: https://rose-ash.com' -H 'Connection: keep-alive' -H 'Referer: https://rose-ash.com/' -H 'Sec-Fetch-Dest: empty' -H 'Sec-Fetch-Mode: cors' -H 'Sec-Fetch-Site: cross-site' -H 'Priority: u=0' --data-raw '{"items":[{"unitPrice":5,"name":"test-1","quantity":2,"rateOfTaxIncludedInPrice":0,"type":"physical","hasSelectedPlan":false}],"targetId":"9434494e-5911-4c37-9c5b-ec225f1820c4","email":"I HID THIS","amount":10,"currency":"gbp","language":"en","billingAddress":{"country":"GB","postalCode":"I HID THIS","city":"south molton","streetAndNumber":"I HID THIS","region":"devon","name":"I HID THIS"},"shippingAddress":{"country":"GB","postalCode":"I HID THIS","city":"south molton","streetAndNumber":"I HID THIS","region":"devon","name":"I HID THIS"},"paymentAuthorizationRedirectUrl":"https://rose-ash.com/snipcart/#/checkout"}'
{"errors":[{"code":"DomainErrors_TargetAlreadyPaid","message":"Target has already been paid. No more payment session can be created for it."}],"type":"","title":null,"status":422,"detail":"","instance":"","extensions":{}}