There can be many reasons why you are not able to post content in some of the channels using the chrome browser extension. Some of the main reasons are:
Archived channel: The channel is archived. User cannot post content in channels which are archived. Channels are archived by organization admin or due to inactivity in that channel for more than 4 weeks.
Restricted permission: You might have insufficient/restricted permission to add content in that channel. You might be a part of the channel as a reader or editor-limited. Or the organization admin has set some permission restriction which is preventing you from posting content in a channel or mix. Please contact your organization administrator for more details.
No standard mixes: The channel might not have any standard mixes where you can post content. Please note that user cannot post or edit content in read-only mixes. You can check the tag of the mixes in your channel
If the tag says ‘read only’ - then the mix is read only and you cannot post any content in that mix.
In case of questions, please feel free to write to us at firstname.lastname@example.org.