Error inserting data into SP list using REST API

Question

I've never seen this error before and I've used REST API many times. I am in SharePoint Online so maybe it behaves differently.

Whenever I insert and item into a list using REST, I get the following error and I don't know why.

Here's a snippet of my code

 $.ajax({
  url: fullUrl,
  method: "POST",
  data: JSON.stringify({
    '__metadata': { 'type': 'SP.Data.Historical_x0020_RegisterListItem' },   //SP.Data.Historical_x0020_RegisterListItem /rr/_api/web/lists/GetByTitle('Register')/ListItemEntityTypeFullName
    'Register': that.register,  //choice column
    'RiskRegister': that.riskRegister,  //choice column
    'Reopen': this.formatDate(that.reopen),  //date column
    'RiskOrIssue': that.riskOrIssue,  //date column
    'Status': that.status,  //choice column
    'problemT': that.probTitle,  //single line of text column
    'ProblemStatement': that.problemStatement,  //multi-line text
    'TaskOwner': that.taskOwner,        //single line of text 
    'Probability': that.probability,  //single line of text
    'Impact': that.impact  //single line of text
  }),
  headers: {
    "accept": "application/json;odata=verbose",
    "content-type": "application/json;odata=verbose",
    "X-RequestDigest": $("#__REQUESTDIGEST").val()
  },
  success: function(){
    alert("Item Added!");
  },
  error: function(data){
    console.log(data);
  } 
  });

Any help with this would be greatly appreciated. Thank you!

Answer 1

Human error on my part. The value to be updated was in lowercase and not capital. Here's the correction:

  'Register': that.Register,  //choice column
    'RiskRegister': that.RiskRegister,  //choice column
    'Reopen': this.formatDate(that.Reopen),  //date column
    'RiskOrIssue': that.RiskOrIssue,  //date column
    'Status': that.Status,  //choice column
    'problemT': that.ProbTitle,  //single line of text column
    'ProblemStatement': that.ProblemStatement,  //multi-line text
    'TaskOwner': that.TaskOwner,        //single line of text 
    'Probability': that.Probability,  //single line of text
    'Impact': that.Impact//single line of text