GARCH models estimation for variance

I have a return series for which i would like to estimate a GARCH(1,1) in order to get volatility accross time. I used this command :

model1 = garch('Offset',NaN,'GARCHLags',1,'ARCHLags',1); [fit1,~,LogL1] = estimate(model1,x); but i have a message error [fit1,~,LogL1] = estimate(model1,x); Warning: Lower bound constraints are active; standard errors may be inaccurate. > In garch/estimate (line 791) Estimated GARCH model is invalid.

Caused by: Error using garch/validateModel (line 782) Non-zero degree P requires a non-zero degree Q.

Can someone help me to deal with. Bests