I am getting the below error when I am doing bulk update.
List has more than 1 row for assignment to SObject

on this line of my code - 
Account acc = [SELECT Email__c FROM Account WHERE Id IN (SELECT AccountId from Opportunity WHERE Id =:Ids)];

My Apex class -

@InvocableMethod
    public static void calculate(List<Id> Ids){
        System.debug('--Id : '+Ids);
            if(!System.isFuture()) {
                CallculateCalloutAsync(Ids);
        }
    } 
    @future(callout=true)
    public static void CallculateCalloutAsync(List<Id> Ids){
        Account acc = [SELECT Email__c FROM Account WHERE Id IN (SELECT AccountId from Opportunity WHERE Id =:Ids)];
        HTTP http = new HTTP();
        HTTPRequest request = new HTTPRequest();
        List<Amount__c> listCS      =       Amount__c.getall().values();   
        if (listCS != null && listCS.size() > 0) {
            String endp                     =       listCS[0].endpoint__c+acc.Email__c;
            String auth                     =       listCS[0].auth__c;
            String authorizationHeader      =       'Basic '+ auth;
            
            request.setHeader      ('Authorization', authorizationHeader);
            request.setEndpoint    (endp);
            request.setMethod      ('GET');
            request.setHeader      ('Content-Type', 'application/json; charset=utf-8');
            HTTPResponse response = http.send(request);
            system.debug('--response : '+response.getBody());
            
            if(response.getStatusCode() == 200){
                system.debug('The Response Body: '+response.getBody());
                Map<String, Object> deserializedPayload = (Map<String, Object>)JSON.deserializeUntyped(response.getBody());
                Decimal balance = (Decimal)deserializedPayload.get('tax');
                Opportunity opp = new Opportunity(Id = Ids[0]);
                opp.amount__c = tax;
                update opp;
            } 
            if(response.getStatusCode() != 200){
                System.debug('The Response Body: '+response.getBody());
                System.debug('No data found!');
            }