Instagram generates specific User ID for each customer that reaches out to you. The User ID for each customer differs per channel. If you try to reach out to a User ID via a different channel then where this was generated, your message will not reach the customer. Let's look at an example below:

I own two different brands, Brand A and Brand B, and have a different Instagram channels set up for each brand. John is my customer and likes to shop at both brands.

• John has reached out to me via the Brand A Instagram channel, where his User ID was generated as 123456789.
• The same John reached out regarding a question to the Brand B Instagram channel, but this time his User ID was generated as 444444444. 

When submitting your API request, you will need to submit both a to and from parameter. The to parameter will contain the channel-specific identifier (123456789 & 444444444 in the examples above) or a MessageBird Contact ID. The from parameter will contain the ID that identifies the channel the message should be sent over. Make sure that, if you are entering a channel-specific identifier, you are entering details that match the right channel.