Hello Jaydeep Suryawanshi,
If you need to increase the message size limit beyond 256 KB, the only option is to upgrade to the Premium tier, which allows messages up to 100 MB.
256 KB for Standard tier 100 MB for Premium tier on AMQP, and 1 MB for Premium on HTTP and SBMP. The maximum size for batches is 256 KB for the Standard tier, and 1 MB for the Premium tier. The message size includes the size of properties (system and user) and the size of payload. The size of system properties varies depending on your scenario.
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Regards,
Abiola