Publishing failed. The response is not a valid JSON response

I am using wordpress 5.4.2. I get this error when trying to add a new post. I changed my permalink to

Post name sample

How should i change my .htaccess

My current htaccess is

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Please help me II am new to wordpress

Akismet Anti-Spam Classic Editor Hello Dolly Increase Maximum Upload File Size Jetpack by WordPress.com myStickymenu OptinMonster API UberMenu 3 – The Ultimate WordPress Mega Menu .These are my installed plugins

This is my custom css

Console error