S3 PutObject returns AccessDenied for PutObject command

[tzmanlfg]

Hoping someone can help.

Having an issue trying to write to an S3 bucket in a different account. Myself and others have gone over the role (sts assumed) and the permissions appear to be correct. Additionally, ListObjects works and CloudTrail shows the KMS key being generated so we are getting to the bucket and kms is allowing encryption.

I am not sure if the request is correct
PutObjectCommandInput
{ "middlewareStack": {}, "input": { "Bucket": "com-a-bucket-dev-feeds", "Body": "{ "value": "success"}", "Key": "datalake/raw/sites/20220127153225490.9CBC8C6F00DF025CE053AC17050DAF8F.json" } }

We are not sending ExpectedBucketOwner.
We are not setting KMS to allow S3 to use what is defined on the bucket.

The error response is:
AccessDenied: Access Denied
at deserializeAws_restXmlPutObjectCommandError (/var/task/app.js:31983:43)
at processTicksAndRejections (internal/process/task_queues.js:95:5)
at async /var/task/app.js:7648:24
at async /var/task/app.js:14753:22
at async StandardRetryStrategy.retry (/var/task/app.js:13621:42)
at async /var/task/app.js:13258:24 {
Code: 'AccessDenied',

Any help would be greatly appreciated