Resume doesn't prompt when using Storyline 2 with Learning Locker LRS

Hi, 

I have created a course through storyline and publish through TIN CAN API to my wordpress website

I extract the zip and upload all the contents to my hosting server, and I create a simple html and embed the story.html through iframe with all the require parameter (endpoint, auth, actor, registration, activity id)

Everything works great except the resume progress  of the course doesn't prompt when I refresh/re-visited the course (webpage). 

I am using the same endpoint, auth actor, registration, and activity id. 

I tried to debug Learning Locker and found that the storyline course is request for application/json content type instead of text/plain. 

Below is the request payload generated for the ../activities/state?method=GET

X-Experience-API-Version=1.0.1&Authorization=Basic cHR0VnBjek9rdzBYRFczdzRSTTo2MU1RdDlXNWhzcENLX3JJM0s0&stateId=resume&Content-Type=application/json&activityId=http://5a8SiBHMf0l_course_id&agent={"mbox":"mailto:xxx@xxx.com","name":"Jason"}

Which I think it should request for text/plain as the content sent it to Learning Locker through (activities/state?method=PUT) is in text/plain.

Below is the request payload for activities/state?method=PUT

X-Experience-API-Version=1.0.1&Authorization=Basic cHR0VnBjek9rdzBYRFczdzRSTTo2MU1RdDlXNWhzcENLX3JJM0s0&stateId=resume&content=2L16806010ji1001211a0101101211~2015000001^1^1^1^1^1^1^1^1^10171^1^1^1^n6OHzsyXsiB3.5Y5cgfspmuA1^1^0a00000000002000&Content-Type=application/json&activityId=http://5a8SiBHMf0l_course_id&agent={"mbox":"mailto:xxx@xxx.com","name":"Jason"}

If it is in JSON format, shouldn't we change the content to example { data:"2L16806010ji1001211a0101101211~2015000001^1^1^1^1^1^1^1^1^10171^1^1^1^n6OHzsyXsiB3.5Y5cgfspmuA1^1^0a00000000002000"}

The resume is working if we change that to text/plain.

Please advise.