@RonakBansal 

To ensure R1 can view and edit the shared field value even when sending to only one recipient initially, you might need to structure your request differently. 

Ensure that both R1 and R2 are defined in the initial API call even if only R1 is meant to act on the document at first. You can specify R2 in a way that they don’t need to take any immediate action.

You can define a signing order where R1 acts first and R2 can come in later, but both need to be part of the envelope to enable collaboration.

@JohnSantos  : But this way, R2 will still receive the email which we do not want.
Isn’t there any other alternative?

As per Docusign guide, If we send the envelope just to limited recipients then it should work.
https://support.docusign.com/s/document-item?language=en_US&rsc_301&bundleId=gbo1643332197980&topicId=lsv1579552570897.html&_LANG=enus
“If you specify only a limited set of recipients, then only those people can collaborate on the field. “

we have a use case where:
Some fields can be edited only by R1
Some fields can be edited only by R2
Sone fields can be edited both by R1 and R2

@RonakBansal 

Then assign fields to specific recipients as follows:

• Editable only by R1: Ensure that these fields are not shared and are assigned specifically to R1.
• Editable only by R2: Ensure that these fields are not shared and are assigned specifically to R2.
• Editable by both R1 and R2: Use shared fields and set up with the tab property shared: true.

@JohnSantos : I have the setup as above but for below shared fields:

Editable by both R1 and R2: Use shared fields and set up with the tab property shared: true.

The field is assigned to R1 and set as collaborative on the Form
So when I send the envelope to R1 only or R1+R2 → It works
But when I send the envelope to R2 → It doesn’t work 

Also, I cannot always the send the email to R2 with no action to take.

I believe there are one or more settings that need to be set when creating envelopes through the api where templates use collaborative fields. Simply setting the “shared” : “true” does not cut it. I have an issue where I add a new(one not listed on the document) signer at envelope creation time that has shared tabs set to true but like your issue, cannot see the fields to.  I’m thinking a collection of shared field signers on the document itself needs to be set or something.