Q:

aws sns publising compressed payload

There is a limit of 256KB as the max size of message which can be published to AWS-SNS.  Can we compress a message using GZIP and send publish the compressed message to overcome the size limit ?  

A:

You already take a look at this?  https://docs.aws.amazon.com/sns/latest/dg/sns-large-payload-raw-message-delivery.html
If you think that the file can increase on the time I suggest another approach. 
Put the file on S3 bucket and attach the S3 Event Notification to SNSTopic so all consumer will be notified when a new file is ready to be processed. 
In other word the message of the SNS will be the location of the file and not the file it self. 
Think about it. 

A:

You can gzip the message body -- however -- SNS message bodies only support UTF-8 character data.   Gzipped data is binary, so that is not directly compatible with SNS because not every possible sequence of bytes is also a valid sequence of UTF-8 characters.   
So, after gzipping your payload, you need to encode that binary data using a scheme such as base-64.   Base-64 encodes arbitrary binary data (8 bits per byte) using only 64 (which is 2^6, giving effectively 6 bits per byte) symbols and so the byte count inflates by 8/6 (133%) as a result of this encoding.   This means 192KB of binary data encodes to 256KB of base-64-encoded data, so the maximum allowable size of your message after gzip becomes 192K (since the SNS limit is 256KB).    But all the base-64 symbols are valid single-byte UTF-8 characters, which is a significant reason why this encoding is so commonly used, despite its size increase.   That, and the fact that gzip typically has a compression ratio far superior to 1.33:1 (which is the break-even point for gzip + base-64). 
But if your messages will gzip to 192K or lower, this definitely does work with SNS (as well as SQS, which has the same character set and size limits).