Error 4901 ERR_BOOKS_CANNOT_ADD when using MarketBookAdd

Code below fails with error 4901 (ERR_BOOKS_CANNOT_ADD)
regardless of broker. But I know such a code worked some time ago.
Possible reason(s)?

string symbol = "EURUSD";
int OnInit() {
        if(SymbolSelect(symbol, true) != false) {
                        printf("market book add failed (%i)", GetLastError());
        else printf("symbol select failed (%s)", symbol);
        return 0;
void OnBookEvent(const string& _symbol) {
        printf("DOM event for %s", _symbol);
void OnDeinit(const int reason) {

You have to choose a broker who provides Depth of Market for EURUSD.


Sure, this is a prerequisite.

However, I can open the DOM manually on each of the brokers I have tested (i.e. FXCM, IronFX, NordFX, MQ demo server), yet the code keeps failing!?

You can open the DOM but no one of the brokers you mentioned provide DOM data.

I see.


Could you advise any broker who provides DOM data?

Noone can give a provider name which offer DOM datas?

Alternatively which is the keyword to search on google a provider name which offer DOM data