Caption that you added to the post, when creating it on desktop, is automatically copied as soon as you click on the Publish Now button in the app on your phone.
Paste the words in the text box by tapping and holding it on the final stage of the publishing process.
Here's an example of the post with a caption:
When you are done with editing, you are directed to the final stage. Tap and hold the text box, hit Paste and there it is: the caption is inserted!
Now, feel free to press Share to actually publish the post.
If you have any further questions, please contact us at [email protected].