How to setup metadata in restapi for insert in SPOnline List

Question

Hi Developers,

I am facing an issue to insert data in sp online list.

I have a scenario, we have lots of columns in sp list within the format of Datafield1,2,3,4 to 50. but on a form user can create a column at a run time in the table according to need by default only 3 columns generated.

how can I set (key and value) in restapi metadata section according to form?

 

Need Urgent help.

 

Thankyou.....