Modifying Product variant details inconsistent

[Mivy]

Hello,

I am new to shopify and new to javascript as well.

What I am trying to achieve is:

1. Create a product and take the variantId from it.

2. Use that variantId and call the variants/{variantId}.json API to modify the title and the price.

I have called both endpoints in one function, and it worked for Creating product, however, the inconsistencies are being seen on Variants. There was only once that the variant update works. 

What am I missing?