[Paytm] Checkout with phone leads to error

[mishrarohit]

On this line https://github.com/activemerchant/offsite_payments/blob/8cd55520f88188242363c751ac0f5b4fbdfa215a/lib/offsite_payments/integrations/paytm.rb#L54

The integration expects an email to always be present on the customer. If the customer checks out with their phone number, email wouldn't be available.

@Mohit-Aggarwal1

[mishrarohit]

How to reproduce

• Navigate to a store with Paytm (for test: https://windia-product.myshopify.com/collections/frontpage/products/inr-1-product)
• Add product to cart and checkout
• In the customer information page, on the email address or phone number field add a phone number instead of an email address
• In the payment method page, select Paytm as the payment gateway and press Continue

Expected Result

The customer should be successfully redirected to Paytm where they can make the payment and get redirected back to Shopify

Actual Result

The customer redirects to Paytm, but then automatically returns back to Shopify's payment method page without any user input with an error message There was an error processing your payment. Please try again Logs show that Paytm return the following response back to the offsite_gateway_callback action:

RESPCODE:803
RESPMSG:Mandatory parameter does not exist with name CUST_ID
STATUS:TXN_FAILURE
MID:Shopif11156290327655
TXNAMOUNT:1.00
ORDERID:146115493890-20180124194448

cc @pi3r

[mishrarohit]

Closed by #275 & #281