Response from flask api giving json parse error in angular

Question

Here my server which is written in flask is basically doing like getting documents from a firebase collection and sending that data(whole data) as a response. My firebase collection have like 9000 documents which I want to send as a response. Here is my flask code -

def getAllCredits(db):
    mainData = []

    try:

        collection = db.collection('Credits')
        docs = collection.stream()
        for index, doc in enumerate(docs):
            res = doc.to_dict()
            mainData.append({"id":doc.id,"data":res})
        print(len(mainData))
        return jsonify(mainData)

Although I am getting all the data as json successfully in postman but in angular I am getting json parsing error. Setting the response type to text is working but I need to get the data as json('Content-Type' also set to 'application/json'). Here is my angular code -

getAllCredits() {
    this.http.get('http://localhost:8080/getAllCredits')
      .subscribe(result => {
        console.log(result);
      })
  }

I am getting error like -

"Http failure during parsing for http://localhost:8080/getAllCredits"
SyntaxError: Unexpected token e in JSON at position 0 at JSON.parse (<anonymous>) at XMLHttpRequest.onLoad (http://localhost:4400/vendor.js:37062:51

Can anybody tell me what is the problem where? Creating the same api in nodejs is working perfectly fine and I am getting all the 9000 documents in angular(JSON parsed correctly). Don't know what is the issue in flask. I am setting the content-type correctly also. Is this issue related for the large data? Can anybody help me regarding this issue?