diff --git a/modules/betweenBidAdapter.js b/modules/betweenBidAdapter.js
index 0ed05717391..f445c9dfd5d 100644
--- a/modules/betweenBidAdapter.js
+++ b/modules/betweenBidAdapter.js
@@ -3,6 +3,7 @@ import { getAdUnitSizes, parseSizesInput } from '../src/utils.js';
 import { getRefererInfo } from '../src/refererDetection.js';
 
 const BIDDER_CODE = 'between';
+const ENDPOINT = 'https://ads.betweendigital.com/adjson?t=prebid';
 
 export const spec = {
   code: BIDDER_CODE,
@@ -30,7 +31,7 @@ export const spec = {
 
     validBidRequests.forEach(i => {
       let params = {
-        sizes: parseSizesInput(getAdUnitSizes(i)).join('%2C'),
+        sizes: parseSizesInput(getAdUnitSizes(i)),
         jst: 'hb',
         ord: Math.random() * 10000000000000000,
         tz: getTz(),
@@ -74,9 +75,14 @@ export const spec = {
         }
       }
 
-      requests.push({method: 'GET', url: 'https://ads.betweendigital.com/adjson', data: params})
+      requests.push({data: params})
     })
-    return requests;
+    return {
+      method: 'POST',
+      url: ENDPOINT,
+      data: JSON.stringify(requests)
+    }
+    // return requests;
   },
   /**
    * Unpack the response from the server into a list of bids.
diff --git a/test/spec/modules/betweenBidAdapter_spec.js b/test/spec/modules/betweenBidAdapter_spec.js
index 94db41ba014..44a8d2cc733 100644
--- a/test/spec/modules/betweenBidAdapter_spec.js
+++ b/test/spec/modules/betweenBidAdapter_spec.js
@@ -20,7 +20,7 @@ describe('betweenBidAdapterTests', function () {
       sizes: [[240, 400]]
     }]
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
     expect(req_data.bidid).to.equal('bid1234');
   });
   it('validate itu param', function() {
@@ -37,7 +37,7 @@ describe('betweenBidAdapterTests', function () {
     }];
 
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
     expect(req_data.itu).to.equal('https://something.url');
   });
@@ -55,7 +55,7 @@ describe('betweenBidAdapterTests', function () {
     }];
 
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
     expect(req_data.cur).to.equal('THX');
   });
@@ -73,7 +73,7 @@ describe('betweenBidAdapterTests', function () {
     }];
 
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
     expect(req_data.subid).to.equal(1138);
   });
@@ -91,7 +91,7 @@ describe('betweenBidAdapterTests', function () {
     }];
 
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
     expect(req_data.click3rd).to.equal('https://something.url');
   });
@@ -111,7 +111,7 @@ describe('betweenBidAdapterTests', function () {
     }];
 
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
     expect(req_data['pubside_macro[param]']).to.equal('%26test%3Dtset');
   });
@@ -134,7 +134,7 @@ describe('betweenBidAdapterTests', function () {
     }
 
     let request = spec.buildRequests(bidRequestData, bidderRequest);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
     expect(req_data.gdprApplies).to.equal(bidderRequest.gdprConsent.gdprApplies);
     expect(req_data.consentString).to.equal(bidderRequest.gdprConsent.consentString);
@@ -217,8 +217,8 @@ describe('betweenBidAdapterTests', function () {
     }];
 
     let request = spec.buildRequests(bidRequestData);
-    let req_data = request[0].data;
+    let req_data = JSON.parse(request.data)[0].data;
 
-    expect(req_data.sizes).to.deep.equal('970x250%2C240x400%2C728x90');
+    expect(req_data.sizes).to.deep.equal(['970x250', '240x400', '728x90'])
   });
 });