Invalid container element error while integrating with third party

I am doing 3rd party integration with yodlee ,and getting the below error Invalid container element .Here is the html code :

<div data-id="container-fastlink" class="container-fastlink">
        <div style="text-align: center;">
            
            <lightning-button class="slds-button slds-button_brand CenterButton" onclick={fastlinkAccount} label="Connect Account" id="btn-fastlink">  </lightning-button>

        </div>

And JS:

 const dynamicContainerId = this.template.querySelector('.container-fastlink').dataset.id;

        console.log('dynamicContainerId is -> ',dynamicContainerId);
        console.log('this.accessToken== ' + this.accessToken);
        var userToken = this.accessToken;
        console.log('usr== ' + userToken);
        console.log('this.fastLinkUrl== ' + this.fastLinkUrl);

        try {

            window.fastlink.open({
                fastLinkURL: this.fastLinkUrl, 
                accessToken: 'Bearer ' + userToken, 
                params: {
                    userExperienceFlow: 'Aggregation',
                    configName: 'Aggregation',
                    forceIframe : true,
                    forceRedirect: true,
                    iframeResize: true
                }, },dynamicContainerId);

Please help me where i am getting wrong?