Statistical Inference — SPRT no-decision probability for exponential mean

Let $X_1, X_2, X_3, …, X_n$ be a sequence of iid observations from an exponential distribution with mean $\frac{1}{\theta}$, $\theta > 0$. To test $H_0 : \theta = 1$ versus $H_1 : \theta = 2$, SPRT is used. What is the probability that the procedure has no decision at the first stage when $\alpha = \beta = 0.1$ and $H_0$ is true?