Retry-After header absent in tab additon senario even if request is throttled

Question

Look at below two responses, one response contains 'Retry-After' header, other does not contain 'Retry-After' header.

Both requests are send to, POST: https://graph.microsoft.com/v1.0/teams/\<teams_id>/channels/<channel_id>/tabs endpoint.

Status code : 429

Does not contain 'Retry-After' header.
Response Headers :
{
'Date': 'Thu, 15 Jul 2021 13:55:46 GMT',
'Content-Type': 'application/json',
'Transfer-Encoding': 'chunked',
'Content-Encoding': 'gzip',
'Vary': 'Accept-Encoding',
'Strict-Transport-Security': 'max-age=31536000',
'request-id': 'f0911923-889d-44b3-b5f3-6558099fee40',
'client-request-id': 'f0911923-889d-44b3-b5f3-6558099fee40',
'x-ms-ags-diagnostic': '{"ServerInfo":{"DataCenter":"South India","Slice":"E","Ring":"2","ScaleUnit":"002","RoleInstance":"MA1PEPF00001470"}}'
}

Response Body :
{
"error": {
"code": "TooManyRequests",
"message": "Failed to execute Skype backend request GetThreadS2SRequest.",
"innerError": {
"date": "2021-07-15T13:55:47",
"request-id": "f0911923-889d-44b3-b5f3-6558099fee40",
"client-request-id": "f0911923-889d-44b3-b5f3-6558099fee40"
}
}

}

Stauts Code: 429

Contains Retry-After header
Response Headers :
{
'Date': 'Thu, 15 Jul 2021 13:55:45 GMT',
'Content-Type': 'application/json',
'Transfer-Encoding': 'chunked',
'Content-Encoding': 'gzip',
'Retry-After': '60',
'Vary': 'Accept-Encoding',
'Strict-Transport-Security': 'max-age=31536000',
'request-id': '17c8990c-5250-4fd9-ac1e-c36e7c1e1a37',
'client-request-id': '17c8990c-5250-4fd9-ac1e-c36e7c1e1a37',
'x-ms-ags-diagnostic': '{"ServerInfo":{"DataCenter":"South India","Slice":"E","Ring":"2","ScaleUnit":"002","RoleInstance":"MA1PEPF000014FF"}}'
}

Response Body :
{
"error": {
"code": "TooManyRequests",
"message": "Too many requests from Identifier:<tenant_id>+<application_id>+<application_id> under category:throttle.teams.ags.api_complex_level_10.tenant_normal.app_normal.operation_write_sustained. Please try again later.",
"innerError": {
"date": "2021-07-15T13:55:45",
"request-id": "17c8990c-5250-4fd9-ac1e-c36e7c1e1a37",
"client-request-id": "17c8990c-5250-4fd9-ac1e-c36e7c1e1a37"
}
}
}

Answer 1

If you do not see a retry-after header, please wait for 10 seconds and retry again.

Answer 2

Use "Exponential Back off strategy" in case of 'Retry-After' header is missing.