402 Payment Required API ERROR

[ahmetb]

We created API to connect with ERP program for warehouse management.

We get 402 Payment Required error when we want to connect. Our shopify plan is active and no payment is required.

Why we get this error ?

 The API we created for order and warehouse management on shopify for marketplace is already working.

is it paid to create a new API?

Can you help us with this, please?