Started a forum - it won't let me post to it

I registered a new account on my Friendica node, and selected the account type as "public forum".

I then logged in with my main account, sent the forum account a friend request (which it accepted).

Then I tried to post on the forum with my main account, but there was no button for posting with? (the button with the pen in it)

I had already made sure the forum account's setting for friends posting on your wall was switched on, and also that we were friends, so I don't understand why it won't let me post to the forum.

Have I done something wrong, or is there some kind of delay with the posting being activated?
You just have to write a new post and mention the Forum in it, if you use the @ mention the post will be delievered to all you contacts and to the forum, if you use the ! mention the post will be delievered to the forum and the forum will then deliever it to all members of the forum. With the ! only one mention, the one with the ! should be used. I guess in most cases the @ metion is a good choice.

I hope I got you right, I understood you looked for some special "form" to write to the forum or write a post in the forum.
It is much better to use the ! for forum posts.
But this only permits to mention 1 forum in each post? Or was it even just one mention at all? I forgot this again.
Mentioning more than a single forum in a post creates some posting distribution chaos. Posting to multiple forums ensures that comments won't reach every subscriber. The forum where a user comments on depends upon the delivery speed of the forum servers, since the first one "wins".