post https://api.shop-and-pay.com/v1.0/Transaction//
Response
xxxxxxxxxx
apiSignature=`echo -n "" | openssl dgst -sha256 -hmac "INSTANCE_API_SECRET" -binary | openssl enc -base64`
curl --request POST "https://api.shop-and-pay.com/v1.0/Transaction/2/?instance=INSTANCE_NAME" \
--data-urlencode "amount=8925" \
--data-urlencode "ApiSignature=$apiSignature"