ProvXchange payments in sandbox

ProvXchange payments in the sandbox behave very similarly to live ProvXchange payments, with some notable differences.

1. ProvXchange payments in the sandbox will settle (i.e. reach a terminal state of completedor failed) approximately 3 minutes after creation. Live ProvXchange payments settle in real-time, typically within minutes.
2. ProvXchange payments to any receiving account number beginning with 0x11111111 will automatically fail.

Organizations are seeded with the following Internal and External accounts for testing.

1. GWB ProvXchange (internal_account)
2. IBB ProvXchange (internal_account)
3. Harry Potter ProvXchange (external_account)
4. Lucius ProvXchange (external_account)