How to post a form in Wordpress?

I am new to Wordpress and I have installed a plugin called simple job board I would like to post candidate data to WordPress. However, I get the following error:-

Unable to write to directory %s. Is this directory writable by the server? Your application could not be processed.

I get this error on my WordPress site. I would like to know how I can post to WordPress job board using a rest API. I am able to fetch data from WordPress now I would like to post some data to WordPress. I am using React js and my WordPress site is hosted on AWS Lighsail. Any help or suggestion is appreciated. Thank you.