There is a conflict with another App, here are the steps to fix this:
1) goto Shopify Admin > Apps > Select "About" on TeleCheckout
2) click "Customize URL"
3) change "checkout-1" to "checkout". Done.
1) goto Shopify Admin > Apps > Select "About" on TeleCheckout
2) click "Customize URL"
3) change "checkout-1" to "checkout". Done.
If it doesn't let you change then there is a conflict with another app, you first need to find which, change its URL to something else, then start again step 1 to 3.