Find an example of a sequence not in $l^1$ satisfying certain boundedness conditions. This question is about getting a concrete example for this question on bounded holomorphic  functions posed by @user122916 (something that he really expected as explained in the comments).
Give an example of a sequence of complex numbers $(a_n)_{n\ge 0}$ so that 
\begin{eqnarray}
|\sum_{n\ge 0} {a_n z^n} | &\le &1  \text{ for all }z \in \mathbb{C}, |z| < 1 \\
\sum_{n\ge 0} |a_n| &=& \infty
\end{eqnarray}
Such sequences exist because there exist bounded holomorphic functions on the unit disk that do not have a continuous extension to the unit circle ( one finds a bounded Blaschke product with zero set that contains the unit circle in its closure). However, a concrete example escapes me. Note that all this is part of the theory of $H^{\infty}$ space, so the specialists might have one at hand.

From  the answer of @zhw. and the comments of @Robert Israel I think we can provide an explicit example as follows:
$$z \mapsto e^{-\frac{1+z}{1-z}}$$  is holomorphic on the unit disk and bounded in absolute value by $1$ ( @zhw. answer)
From the comment of @Robert Israel we get the explicit series expansion
$$e^{-\frac{1+z}{1-z}} = e^{ -1 -\frac{2z}{1-z}} = e^{-1} \cdot \sum_{n\ge 0} L^{(-1)}_n(2)\,  z^n$$
where $L^{(\alpha)}_n(x)$ are the Laguerre polynomials.
We have asymptotics  for the Laguerre polynomials. Some numerical testings suggest the following explicit bound:
$$ \frac{L^{(-1)}_n(2)}{e}  - \frac{2^{1/4} }{\sqrt{\pi}} \frac{\cos(\sqrt{8n} + \frac{\pi}{4}) }{n^{3/4}} = \theta_n\cdot n^{-5/4}$$
with $|\theta_n| \le \frac{1}{7.2}$   ($n \ge 1$). 
We conclude that for all $z$ in $\mathbb{C}$, $|z| <1$ we have 
$$\left|\sum_{n\ge 1} \frac{\cos(\sqrt{8n} + \frac{\pi}{4}) }{n^{3/4}}\, z^n\right | < \frac{\sqrt{\pi}}{2^{1/4}}\cdot (\, 1/e + 1 + \frac{5}{36} \zeta(5/4)\,) = 2.9899..<3$$
