# 400 "unable to deserialize" / "error parsing request body" when calling messages.send

**URL:** <https://forums.nylas.com/t/400-unable-to-deserialize-error-parsing-request-body-when-calling-messages-send/1126>\
**Category:** Question and Answers\
**Tags:** email-api\
**Created:** [March 31, 2026, 3:02pm UTC](https://forums.nylas.com/t/400-unable-to-deserialize-error-parsing-request-body-when-calling-messages-send/1126 "2026-03-31T15:02:49Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![aleksey](https://avatars.discourse-cdn.com/v4/letter/a/bc8723/32.png) [@aleksey](https://forums.nylas.com/u/aleksey)\
**Post date:** [March 31, 2026, 3:02pm UTC](https://forums.nylas.com/t/400-unable-to-deserialize-error-parsing-request-body-when-calling-messages-send/1126/1 "2026-03-31T15:02:49Z")

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Hi,

I’m sending email with the Node SDK (`nylas@8.0.5`) and I keep getting a 400 from `messages.send`.

Provider/API side error (Microsoft):

`400 unable to deserialize`  
`error parsing request body`

I’m using the v8 SDK like this:

`await nylas.messages.send({`  
` identifier: grantId,`  
` requestBody: {`  
` from: [{ name: 'Sender', email: 'sender@example.com' }],`  
` to: [{ name: 'Recipient', email: 'recipient@example.com' }],`  
` replyTo: [{ name: 'Reply', email: 'reply@example.com' }],`  
` subject: 'Test',`  
` body: '<p>Hello</p>',`  
` },`  
`})`

Request id where i’ve got this error first today is: 3431756385-1e4739b8-9659-469e-98b7-a5a32acb2304

I also tested without replyTo and still got the same error. No attachments are used.

A few questions:

1. Are there known cases where Nylas returns provider returned error + unable to deserialize even when the JSON looks valid?

2. Is there a way to get the raw request validation error from Nylas, or more detailed provider-side diagnostics?

3. Maybe a bug in Nylas to Microsoft integration somewhere?

Thanks.

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<div class="post-metadata">

**Author:** ![Samuel.R](https://avatars.discourse-cdn.com/v4/letter/s/6bbea6/32.png) [@Samuel.R](https://forums.nylas.com/u/Samuel.R)\
**Post date:** [March 31, 2026, 3:14pm UTC](https://forums.nylas.com/t/400-unable-to-deserialize-error-parsing-request-body-when-calling-messages-send/1126/2 "2026-03-31T15:14:39Z")

</div>

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<div class="post-metadata">

**Author:** ![Samuel.R](https://avatars.discourse-cdn.com/v4/letter/s/6bbea6/32.png) [@Samuel.R](https://forums.nylas.com/u/Samuel.R)\
**Post date:** [March 31, 2026, 3:14pm UTC](https://forums.nylas.com/t/400-unable-to-deserialize-error-parsing-request-body-when-calling-messages-send/1126/3 "2026-03-31T15:14:46Z")

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